Effects of tourism-derived sewage on coral reefs: Isotopic assessments identify effective bioindicators
2019
Lachs, Liam | Johari, Nur Arbaeen Mohd | Le, Dung Quang | Safuan, Che Din Mohd | Duprey, Nicolas N. | Tanaka, Kentaro | Hong, Tan Chun | Ory, Nicolas C. | Zainudin Bachok, | Baker, David M. | Kochzius, Marc | Shirai, Kotaro
Pulau Redang and Pulau Tioman have experienced huge tourism growth over the last two decades, but minimal sewage treatment may threaten the resilience of their coral reefs. This study uses stable isotope techniques to identify suitable bioindicators of sewage nutrients (δ¹⁵N) at these islands by measuring macroalgae (Lobophora spp.), gastropods (Drupella spp.), scleractinian coral (Acropora spp.), and leather coral (Sinularia spp.). At tourist hubs using seepage septic tank systems, enrichment of Acropora δ¹⁵N (Redang, +0.7‰) and Sinularia δ¹⁵N (Tioman, +0.4‰) compared to pristine background levels indicate enhanced sewage nutrient discharge. Carbon isotopes and survey data suggest that sedimentation did not confound these δ¹⁵N trends. Potential damaging effects of sewage discharge on the coral reef communities at both islands are highlighted by strong correlations between Acropora δ¹⁵N and regional variation in coral reef community structure, and exclusive occurrence of degraded reefs at regions of high sewage influence.
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